The invention relates to an electric drive unit, in particular for windshield wipers of a motor vehicle, including a drive motor having an armature accommodated in a substantially cup-shaped pole housing, having a substantially cup-shaped gearbox, secured on its face end to the pole housing, for receiving gear elements that convert the rotation of an armature shaft of the armature, supported on one end in the pole housing and on the other in the gearbox.
One such drive unit is known for instance from German Patent Disclosures IDE 32 20 191 A1, DE 32 35 622 A1, and IDE 41 16 100 A1, and from German Patent DE 39 30 144 C2.
In these known drive units, to support the armature shaft in the pole housing a spherical cap bearing of a sintered metal is used, which is fixed in the pole housing in an indentation by means of a spring washer adapted to the bearing. Because the spherical cap can rotate, slightly skewed positions of the armature do not disadvantageously affect the running properties of the drive unit.
One problem in such a drive unit is the complicated assembly of the spherical cap bearing, which requires additional securing elements in the form of spring washers or the like. It is therefore the object of the invention to refine an electric drive unit, in particular for windshield wipers of a motor vehicle, of the above-defined generic type in such a way that simple mounting of the armature shaft in the pole housing with as few parts as possible, and consequently also the simplest possible assembly of the drive unit, are made possible.
The objects of the invention are attained in an electric drive unit of the type described at the outset, according to the invention in that the armature shaft, adjacent to a bottom of the pole housing, is supported in a cylindrical bearing mounted in the pole housing with a press-fit, wherein the outer diameter of the bearing is greater than or equal to three times its length.
In this invention, a cylindrical bearing is mounted by a press fit, wherein the outer diameter of the bearing is just slightly greater than the space in which it fits, so that the bearing must be pressed into place. This cylindrical bearing supports the armature shaft in the pole housing. Further, the outer diameter of the cylindrical bearing is greater than or equal to three times its length. This has the especially great advantage that because of the press fit of the bearing, wherein the bearing has a slightly greater external diameter than the space into which it fits, additional securing elements, such as spring washers and the like, can be dispensed with. Because the outer diameter is greater than or equal to three times the bearing length, virtually no reduction in the inside diameter occurs during mounting of the cylinder bearing by a press fit. Also because the outside diameter of the bearing is substantially greater than its length, even slightly skewed positions of the armature shaft do not have a disadvantageous effect on the running properties of the overall drive unit.
A cylinder bearing with such dimensions also makes a compact structure possible, that is, a reduction in installation space and in particular a shortening of installation space both for the pole housing and the armature shaft, and this makes it possible to economize on material.
Purely in principle, the cylinder bearing can be secured in the most various ways in the pole housing. For instance, special bearing receptacles may be provided in the pole housing.
An especially advantageous embodiment provides that the cylindrical bearing is disposed in an indentation embodied in the pole housing bottom. This indentation may be produced advantageously in the pole housing, which is usually made as a deep-drawn part.
Since moreover a large bearing seat diameter for the cylinder bearing is necessary in the pole housing, it is assured that the armature winding of the drive motor, because of the large-diameter indentation necessary for such a large bearing seat diameter, cannot collide with the pole housing bottom, and thus in this sense a compact design of both motor and pole housing is possible.
It is also advantageously provided that the body of the cylinder bearing acts as a lubricant repository. Once again, it is especially advantageous that the outer diameter of the cylinder bearing is substantially greater than its length. Because of the large outer diameter of the bearing, an adequate pore volume in the body of the cylinder bearing, which acts as a lubricant repository, is thus created with a short bearing length.